Question

Which of the following drugs inhibit(s) ATP-ADP translocase?

• A. Oligomycin
• B. Atractyloside
• C. Amytal
• D. Bongkrekic acid

Hint:

Only two of the four drugs bind the adenine nucleotide translocator itself; the others target ATP synthase or Complex I instead.

Answer 1

The Correct Option is B, D

Step 1: Recall what ATP-ADP translocase does.
ATP-ADP translocase, also called the adenine nucleotide translocator (ANT), sits in the inner mitochondrial membrane. It exchanges ADP made in the cytoplasm for ATP made inside the mitochondrial matrix by ATP synthase, one molecule at a time in opposite directions. Without this exchange, ATP made in the matrix could never reach the cytoplasm where the cell actually uses it.

Step 2: Go through each drug and its known target.
Oligomycin binds to the \(F_o\) subunit of ATP synthase itself, blocking the flow of protons through the enzyme and stopping ATP synthesis directly, not the transport step. Amytal (amobarbital) blocks Complex I (NADH dehydrogenase) of the electron transport chain, preventing electrons from NADH from entering the chain. Atractyloside is a plant toxin that binds the adenine nucleotide translocator from the cytoplasmic (outer) side and locks it in a conformation that cannot bind ATP, directly blocking the ADP/ATP exchange. Bongkrekic acid is a bacterial toxin that also targets the adenine nucleotide translocator, but it binds from the matrix side and locks the carrier in the opposite conformation, again preventing the exchange, but by freezing the transporter facing inward instead of outward.

Step 3: Identify the translocase-specific inhibitors.
Only atractyloside and bongkrekic acid act directly on the ATP-ADP translocase; the other two drugs act on different components of oxidative phosphorylation (ATP synthase and Complex I respectively).

Step 4: Rule out the other options.
Oligomycin is an ATP synthase inhibitor, not a translocase inhibitor; though blocking synthase indirectly stops ATP export too, its direct binding site is different. Amytal blocks electron transport at Complex I, well upstream of the translocator, and has no direct effect on nucleotide exchange.

Final Answer:
Atractyloside and Bongkrekic acid directly inhibit the ATP-ADP translocase. \[ \boxed{\text{Atractyloside and Bongkrekic acid}} \]